Vehicles may include cooling systems configured to reduce overheating of an engine by transferring the heat to ambient air. Therein, coolant is circulated through the engine block to remove heat from the hot engine, and the heated coolant is then circulated through a radiator near the front of the vehicle. Heated coolant may also be circulated through a heat exchanger to heat a passenger compartment. The cooling system may include various components such as various valves and one or more thermostats.
One example of an engine coolant system is shown by Stang et al. in U.S. Pat. No. 4,325,219. Therein, the coolant system includes an engine loop and an aftercooler loop, coolant circulated through both loops via a single engine-driven pump. The engine loop includes the pump, the engine block, a first radiator, and a radiator bypass branch. The aftercooler loop includes the pump, the aftercooler, a second radiator, and a radiator bypass branch. Each loop further includes a temperature responsive flow control thermostat for regulating coolant flow through the associated radiator and/or bypass branch. The thermostat responds to the temperature of the coolant leaving the aftercooler. In still other examples, grille shutters coupled to a front end of the vehicle may be opened to expedite engine cooling.
However, the inventors herein have recognized potential issues with such systems. As one example, the system may have an elevated power consumption, which renders the engine fuel inefficient. For example, the inventors have recognized that the intermittent turning on and off of the radiator fan may be energy intense. Additional energy losses may occur when the pump is running while grille shutters are opened due to the increase in drag experienced due to grille shutter operation. Likewise, more energy may be consumed when the pump is operated while running the radiator fan(s). Even in engine systems where the pump speed can be independently controlled via an electric motor, the power usage may not be efficient.
Inefficiencies may originate from several causes. As a first example, inefficiencies may be caused from pumping against a closed or partially closed thermostat since this impedes the flow that the controller is trying to establish. As another example, pumping a radiator to provide a greater flow rate than needed to achieve a target engine outlet (or cylinder head) temperature wastes pumping power. As yet another example, operating the radiator fan at a higher speed than required to achieve a target radiator temperature drop wastes fan power. Cycling the radiator fan or radiator pump is also more power consumptive because the fluid power increases with the cube of velocity, faster than the heat transfer increases with velocity. Inefficiencies are also caused by aerodynamics being affected by the grille shutter being open.
The inventors herein have recognized that both radiator pumping and radiator fan operation is required to reject significant heat power. Zero coolant flow with the fan running results in no cooling. Likewise, zero air flow with the coolant pumping also provides no cooling. In other words, both are needed and at the same time. The radiator coolant pump accounts for nearly all the coolant flow since the natural convection is minimal in the engine. The radiator air cooling can be significant at cold ambient and/or at high vehicle speed. By allocating power to the radiator coolant pump versus the radiator fan so as to maintain a target minimum radiator temperature drop (engine outlet temperature minus radiator outlet temperature) via the radiator fan and grille shutters allows engine cooling to be provided while minimizing the power losses. Then, the radiator coolant pump can be controlled to achieve the target engine coolant outlet temperature.
In one example, engine cooling may be provided more efficiently by an engine coolant system comprising: a first pump coupled between a thermostat and a cylinder head; a second pump coupled between the thermostat and a radiator fan; grille shutters; a first temperature sensor for sensing coolant temperature at a radiator outlet; and a second temperature sensor for sensing the coolant temperature at a radiator inlet. The system may further comprise a controller including computer-readable instructions stored on non-transitory memory for adjusting an output of the first pump based on engine power, the first pump operated independent of a state of the thermostat; and selectively operating the second pump responsive to the thermostat being open. In this way, engine cooling can be provided in a more power efficient manner.
As one example, an engine cooling system may be configured to include a first electrically powered circulation pump, a second electrically powered radiator pump, a radiator fan, and grille shutters. An additional pump may be optionally included for circulating heat through a cabin heating loop. The first pump may be separated from the second pump in a coolant loop via a thermostat valve. The fully-open temperature of the thermostat valve may be set to be below the target engine coolant temperature (ECT). In addition, the system may include a plurality of sensors such as an engine coolant temperature (ECT) sensor, a cylinder head temperature (CHT) sensor, a radiator inlet temperature (RIT) sensor, and a radiator outlet temperature (ROT) sensor. By including two pumps, the jobs of circulating coolant and radiator pumping are distributed between the pumps. In particular, the circulation pump may be selectively coupled to the engine block and may be operated to maintain substantially isothermal conditions at the engine. This reduces the occurrence of hot spots near the cylinder heads. The circulation pump is controlled, open loop, as a function of a difference between ECT and CHT. Alternatively, the circulation pump output may be adjusted as a function of engine power. This allows the circulation pump to be operated to reduce the ECT to CHT difference to (or below) a threshold value. The radiation pump is coupled to the radiator, and is selectively coupled to the engine block when the thermostat valve is open. The radiation pump is operated to achieve a target engine temperature (e.g., a target CHT). In particular, the radiator pump may be selectively operated only when the thermostat valve is fully open, thereby reducing energy being wasted in pumping against a fully or partially restricted valve. Since the target ECT is selected to be above the thermostat fully open temperature setting, the thermostat effectively acts as a device that blocks flow for cold and warm coolant, enhancing cylinder head warm-up. When the thermostat valve is open, the radiator pump is the primary effector for controlling engine temperature. The radiator fan and grille shutters are operated to improve the efficiency of the radiator, such as by maintaining a target temperature drop across the radiator. For example, the radiator fan speed is controlled as a function of the difference between RIT and ROT.
In this way, engine cooling is provided while reducing the overall power consumption of the engine cooling system. The technical effect of separating engine cooling functions between a circulation pump operated distinct from a radiator pump is that heat transfer at the cylinder head can be optimized independent of optimizing heat loss at the radiator. By using the circulation pump to maintain a threshold temperature difference between coolant temperature and engine temperature, cylinder head hot spot occurrence is reduced. By using the radiator pump to regulate the coolant temperature to a target setting, radiator operation may be better coordinated with engine heating/cooling operations. By operating the radiator pump only when the thermostat valve is open, cycling of the radiator pump is reduced, decreasing associated power losses. Likewise, by controlling the grille shutters and radiator fan to provide a target temperature difference across the radiator, cycling of the fan and the grille shutters is reduced, decreasing associated power losses. In particular, the power losses associated with cycling the radiator fan on and off is reduced by operating the radiator fan constantly at a lower speed. By reducing power losses across the engine cooling system, the efficiency of the engine cooling system is improved, improving overall engine fuel economy. Overall, engine cooling hardware can be configured to allow for a minimum energy to be expended on cooling an engine while implementing a control approach that minimizes the power spent on cooling the engine.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.